A panel-test evaluation of an acoustical material is generally made with the material, in the form of a slab, attached to a stiff support plate. However, measured acoustic transmission and reflection characteristics of the panel comprising the material and the support plate are not the intrinsic acoustic characteristics of the acoustical material. Rather, these characteristics are indicative only of the acoustic behavior of the material when it is attached to a particular support plate and immersed in the particular fluid medium in which the panel test is conducted. An analytic method is described that can be used to obtain, from the results of a panel test in which an acoustical material is evaluated while attached to a support plate, the intrinsic acoustic properties of the material. This is done by analyzing an equivalent-circuit analog network that describes the panel. A general one-dimensionally nonhomogeneous acoustical material is considered in this analysis. The acoustic properties of such a material may vary in an arbitrary way in the direction perpendicular to the faces of the slab of material that is being evaluated, but in any plane parallel to the slab faces, these properties are considered to be the same everywhere. The analysis shows that the intrinsic properties that determine the acoustic behavior of such a nonhomogeneous material can be specified in terms of three impedances. These impedances can be determined from the two complex pressure reflection coefficients and the complex pressure transmission coefficient measured in a panel test made with the material attached to the support plate. The values of these impedances are, however, independent of the nature of the support plate and of the fluid surrounding the panel when the acoustical material is evaluated. That is, by using the method presented, one can analytically remove the effects of the support plate and the surrounding fluid from the panel-test results. Consequently, once the impedance values specifying the acoustical material are obtained, the analysis shows that it is possible, in principle, to predict the acoustic performance of the material in a wide variety of different circumstances. Some implications of the analysis in the case of effectively homogeneous acoustical materials are also examined. In particular, it is shown how the complex sound speed characterizing such a material can be obtained by panel-test measurements.